In a conventional screen printing machine, correction of the position of a printing screen with respect to an article to be printed (hereinafter referred to as "printed article") such as a substrate for an electronic component or the like, is carried out by means of a mechanism for concurrently adjusting three axes. This mechanism thus corrects the position of the screen in a lateral direction (X-axis correction), it corrects the position thereof in a longitudinal direction perpendicular to the lateral direction (Y-axis correction), and it corrects the position thereof in a rotational direction (.theta.-axis correction). Such a conventional position adjusting mechanism is shown in FIG. 4 by way of example. More particularly, the mechanism includes a first adjustment member 3 arranged for laterally moving a screen frame 2 mounted thereon with a screen printing mask or printing screen 1 to carry out X-axis correction of the printing screen 1, as well as second and third adjustment members 4 and 5 arranged in juxtaposition to each other for moving the screen frame 2 in a longitudinal direction to carry out Y-axis correction of the printing screen 1. The second adjustment member 4 and third adjustment member 5 are also constructed so that the amount of correction by the members 4 and 5, respectively, are different from each other in order to concurrently carry out correction of the printing screen 1 in a .theta.-axis direction.
Thus, the conventional position adjusting mechanism shown in FIG. 4 is adapted to concurrently adjust the three X-, Y- and .theta.-axes, so that adjustment of each of these axes leads to a variation in correction of the remaining axes. For example, changes in the amounts of correction of the second and third adjustment members 4 and 5 for the .theta.-axis correction will require a variation in the amount of Y-axis correction, as well as the x-axis correction. This fails to facilitate printing position correcting, resulting in the operation being troublesome and time consuming.
The present invention is an attempt to overcome the foregoing disadvantages of the prior art. Accordingly, it is an object of the present invention to provide a method and an apparatus for correcting a screen position during screen printing, which are capable of accomplishing correction of a printing position in a short period of time by independently carrying out correction of a position of a screen frame in a rotational direction, or .theta.-axis correction of the screen frame, the screen frame having a printing screen mounted thereon.
This and other objects and the novel features of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of a preferred embodiment of the invention. cl SUMMARY OF THE INVENTION
In accordance with the present invention, these and other objects have now been realized by the invention of a method for adjusting the position of a printing screen having a center of rotation mounted on a screen frame for use in a screen printing process comprising rotatably supporting the screen frame at a plurality of locations on a screen frame holder and rotating the screen frame around the center of rotation by means of an adjustment member associated with the screen frame holder in order to correct the position of the printing screen with respect to the center of rotation. In accordance with one embodiment of the method of the present invention, the method includes fixing the screen frame to the screen frame holder after correcting the position of the printing screen.
In accordance with another embodiment of the method of the present invention, the screen frame has x and y axes, and the method includes further correcting the position of the printing screen by altering the position of the screen frame along the x and y axes.
In accordance with another embodiment of the method of the present invention, adjusting of the position of the printing screen is carried out with respect to an article to be screen printed, the article being mounted on a table having x and y axes, and the method including further correcting the position of the printing screen by altering the position of the table along the x and y axes.
In accordance with another embodiment of the method of the present invention, rotating of the screen frame includes elastically biasing the screen frame against the rotating to control the rotating step.
In accordance with the apparatus of the present invention, apparatus has been discovered for adjusting the position of a printing screen having a center of rotation for use in a screen printing process comprising a screen frame with the printing screen mounted thereon, a screen frame holder, a plurality of first arcuate guide members mounted on the screen frame and defining an arc having a predetermined circumference defined by a predetermined radius, a plurality of second guide members mounted on the screen frame holder, the plurality of second guide members corresponding to the plurality of first arcuate guide members, whereby the plurality of second guide members movably supports the plurality of first arcuate guide members, and an adjustment member adapted to urge the screen frame around the center of rotation of the printing screen. Preferably, the plurality of second guide members comprises a plurality of guide rollers.
In accordance with one embodiment of the apparatus of the present invention, the apparatus includes fixing means for fixing the position of the screen frame with respect to the screen frame holder.
In accordance with another embodiment of the apparatus of the present invention, the apparatus includes a screen frame biasing member for biasing the screen frame in a direction towards the adjustment member.
In accordance with another embodiment of the apparatus of the present invention, the adjustment member comprises a first support member mounted on the screen frame holder, an adjustment screw threadably inserted into the first support member, a first slide member slidable with respect to the first support member and engaged with the adjustment screw, and an abutment member mounted on the slide member for abutment against the screen frame. In a preferred embodiment, the abutment member comprises an abutment roller.
In accordance with another embodiment of the apparatus of the present invention, the screen frame biasing member comprises a second support member mounted on the screen frame holder, a second slide member slidable with respect to the second support member, a receiving member mounted on the second slide member and in contact with the screen frame, and a spring for biasing the second slide member towards the screen frame, whereby the receiving member is maintained in contact with the screen frame. In a preferred embodiment, the receiving member comprises a receiving roller rotatably mounted on the second slide member.
In accordance with one embodiment of the present invention, a method for correcting the screen position in screen printing processes is provided. The method of the present invention includes the steps of rotatably supporting a screen frame, which has a printing screen mounted thereon, at a plurality of locations on a screen frame holder; and urging the screen frame in a direction which deviates from a center of rotation of the screen frame by means of an adjustment mechanism mounted on the screen frame holder, to thereby rotate the screen frame, resulting in correcting a position of the screen in a direction of rotation thereof.
In accordance with another aspect of the present invention, an apparatus for screen position correcting in screen printing is provided. The apparatus of the present invention includes a screen frame having a printing screen mounted thereon; a plurality of arcuate guide members each fixedly mounted on the screen frame in a manner to define an arc of an identical circumference having a predetermined radius; a screen frame holder; guide roller mounted on the screen frame holder so as to correspond to the respective arcuate guide members and arranged so as to movably support the respective arcuate guide members thereon; an adjustment mechanism arranged on the screen frame holder so as to force the screen frame in a direction which deviates from a center of rotation of the screen frame; and fixing means for fixing the screen frame at a predetermined position with respect to the screen frame holder.